The invention relates to a method and a system for transferring data between at least one read/write device and at least one mobile data memory in an identification system with at least one mobile data memory attached to at least one object, for detecting object-related data of the at least one object.
Identification systems known from the prior art include at least one stationary read/write device for contactless data exchange with mobile data carriers, typically by means of a radio-based data transfer link. Such systems are used in technical installations where a plurality of objects or goods must be moved, and possibly otherwise processed, as quickly and freely as possible. The objects can range through the widest variety of types, e.g. packages in a dispatch system, assembly components in a manufacturing system, luggage in a transport system, moving vehicles, etc. As a rule it is necessary, at defined locations within the system, e.g. a manufacturing plant, to determine quickly and freely, for instance, the type, condition, and/or status of the objects actually found in spatial proximity to these locations. For this purpose, the objects on the one hand are provided with mobile data memories, which contain, for instance, data that identifies the type, condition, and/or current status of the objects. On the other hand, read/write devices are placed at the defined locations within the system and are frequently connected to central data processing equipment.
If such objects, e.g. in the course of manufacture, are transported into spatial proximity of a selected location, the stationary read/write device that is arranged there can contactlessly detect and, if necessary, change the data in the mobile data memories of the objects that are currently within its detection range. The data can then be evaluated for various purposes by means of higher-level central data processing equipment, e.g. to track the path of the objects that are provided with the mobile data memories and, as a function thereof, to control operational equipment of the corresponding technical system.
In technical installations, the objects or goods provided with mobile data memories are usually moved along predefined paths with the aid of technical transport means, e.g. conveyor belts. The paths of these transport means can ran closely spaced together or be superimposed or run in parallel. To detect the flow of the objects along the respective paths, read/write devices may be assigned to the paths. Mostly to monitor and control the flow of the objects, these read/write devices have the function to exchange data with the mobile data memories attached to those objects that are being transported along the corresponding path or by the corresponding transport means.
In such situations, the problem may arise that a read/write device inadvertently exchanges data with a mobile data memory attached to an object that is being moved along a non-corresponding but spatially adjacent path. There may be a wide variety of causes for this, e.g. poor mechanical configurations, overreach, reflection effects, and fluctuations in the position of the individual objects on the respective transport path. Thus, in many cases where mobile data memories are used, for instance, to control and track goods, it is necessary to limit the location of corresponding mobile data memories in order to prevent miscommunications.
To avoid such miscommunications, various methods are known and used in the art.
In a first method, the detection area or communication range of the read/write devices is limited. This prevents any unwanted communication with mobile data memories that are located, for instance, in an adjacent assembly line. In practice, wren however, limiting the detection range also strongly limits the possible applications of such an identification system. Nor is it always possible in practice to distinguish mobile data memories in this manner with sufficient reliability. The reason for this, on the one hand, is the width of e.g. the assembly lines. They require a sufficiently large communication range of the read/write devices to permit reliable identification of objects and their data memories that are traveling in rapid succession and/or are poorly positioned on the conveyor belt. On the other hand, conveyor belts in manufacturing plants are often spaced so tightly together that it is difficult to avoid crosstalk of the communication range of read/write devices on one conveyor belt to an adjacent conveyor belt.
In a second method, the communication range of the read/write devices is not limited, but additional status information is kept available in the individual mobile data memories. This makes it possible to ensure that communication between a read/write device and mobile data memories can take place only in a fixed sequence. These types of data memories, however, cannot be used universally. Furthermore, additional physical measures to protect against overreach are nevertheless required, particularly at the beginning of a data exchange.
In yet another method, the communication range of the read/write devices is also not limited. By measuring the signal level of the data streams sent by the mobile data memories, their distance from the corresponding read/write device is estimated. This makes it possible to decide whether a data stream comes from a corresponding or from a foreign mobile data memory. This method has the particular drawback, however, that it cannot be used in closed spaces, such as factory bays, i.e. in indoor applications. The reason for this is that, due to multiple reflections in buildings, there can be strong fluctuations in the received field strength. As a result, a determination of the range by evaluating signal levels is subject to too much error.